This application is based on Japanese Patent Application No. 11-270355 filed Sep. 24, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a method of producing a body member for a piston for a awash plate type compressor, and more particularly to a method of producing, by die-casting, such a body member having a hollow cylindrical head portion.
2. Discussion of the Related Art
A swash plate type compressor is adapted to compress a gas by a plurality of pistons which are reciprocated by a rotary movement of a swash plate. In general, the piston includes a head portion slidably fitted in a cylinder bore formed in a cylinder block of the compressor, and an engaging portion which sidably engages the swash plate. For reducing the weight of the piston, it has been proposed to form the piston with a hollow cylindrical head section. As one example of the method of producing such a piston, the assignee of the present invention proposed in JP-A-11-152239 a method of producing a blank for the piston, comprising the steps of preparing a body member including a hollow head section which is closed at one of its opposite ends and is open at the other end, and an engaging section which is formed integrally with the head section; and fixing a closing member prepared separately from the body member, to the body member so as to close the open end of the head section. While the closing member may be produced by any method, the body member is preferably produced by die-casting.
The present invention was made in the light of the background art described above. It is an object of the present invention to provide a single-headed piston for a swash plate type compressor, which has a reduced operating noise.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that: the outer circumferential surface of the head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of the cylindrical surface, so as to smoothly extend from at least one circumferential part of the cylindrical surface, the curved surface being formed such that a radial distance between a centerline of the cylindrical surface and the curved surface gradually decreases in an axial direction of the cylindrical surface from the corresponding axial end of the cylindrical surface toward the corresponding axial end of the piston, and such that a radius of curvature of a cross sectional shape of the curved surface taken in a plane which includes the centerline of the cylindrical surface is larger than a diameter of the inner circumferential surface of the cylinder bore.
The curved surface formed adjacent to at least one of axially opposite ends of the cylindrical surface of the head portion of the single-headed piston is effective to reduce the noise generated by the awash plate type compressor during its operation. The presence of the curved surface permits the head portion of the piston to smoothly slide on the inner circumferential surface of the cylinder bore.
(2) A single-headed piston according to the above mode (1), the curved surface is formed at at least one of an axial end of the cylindrical surface nearer to the engaging portion so as to extend from a first circumferential part of the cylindrical surface which is nearer to an axis of rotation of the swash plate, and an axial end of the cylindrical surface remote from the engaging portion so as to extend from a second circumferential part of the cylindrical surface which is more distant from the axis of rotation of the swash plate than the first circumferential part.
The above-indicated first and second circumferential parts of the cylindrical surface of the head portion of the piston generally suffer from a particularly large contacting surface pressure when the head portion of the piston contacts the inner circumferential surface of the cylinder bore during operation of the swash plate type compressor. By forming the curved surfaces in these circumferential parts, the piston can be smoothly reciprocated within the cylinder bore.
(3) A single-headed piston according to the above mode (2), wherein the curved surface is formed at the axial end of the cylindrical surface which is remote from the engaging portion and extends over an entire circumference of the cylindrical surface.
It is confirmed that the curved surface formed at the axial end of the head portion of the piston which is remote from the engaging portion is particularly advantageous. In general, the axial end face of the head portion remote from the engaging portion has a simple circular configuration. Since the cylindrical surface and the circular end face intersect each other so as to define a simple circle, it is easy to form the curved surface which extends over the entire circumference of the cylindrical surface of the head portion at the axial end which is remote from the engaging portion.
(4) A single-headed piston according to the above mode (2) or (3), wherein the curved surface is formed at one of opposite axial ends of the head portion which is nearer to the engaging portion and extends over an entire circumference of the axial end of the head portion.
Where the single-headed piston has a hollow cylindrical head portion, the axial end of the outer circumferential surface of the head portion which is nearer to the engaging portion has a simple circular shape. Accordingly, it is easy to form the curved surface which extends over the entire circumference of the outer circumferential surface at that axial end. However, the curved surface which extends over the entire circumference of the outer circumferential surface may be formed at that axial end portion whose configuration is not a simple circle.
(5) A single-headed piston according to any one of the above modes (1)-(4), wherein the cross sectional shape of the curved surface taken in the plane which includes the centerline of the cylindrical surface is an arc.
The cross sectional shape of the curved surface may be suitably determined, provided it has a smooth convex curve. For instance, the cross sectional shape of the curved surface may be a plurality of arcs having respective different radii of curvature, an ellipse, or a part of a hyperbola. If the cross sectional shape of the curved surface is a simple arc, the piston can be economically manufactured.
(6) A single-headed piston according to any one of the above modes (1)-(5), wherein a dimension r1 between a surface of extension of the cylindrical surface and a straight line which is parallel to the surface of extension and which passes one of opposite ends of the curved surface which is remote from the cylindrical surface is not greater than 15 xcexcm.
When the dimension r1 is excessively large, the lubricant oil adhering to the inner circumferential surface of the cylinder bore is less likely to be introduced into a wedge-shaped gap which is formed between the inner circumferential surface of the cylinder bore and the outer circumferential surface of the head portion of the piston. In this case, the effect of the formed curved surface is reduced. In view of this, the above-indicated dimension r1 is generally not greater than 15 xcexcm, preferably not greater than 10 xcexcm, and more preferably not greater than 5 xcexcm. On the contrary, if the dimension r1 is excessively small, the lubricant oil is less likely to be introduced into the wedge-shaped gap. Accordingly, the dimension r1 is preferably not smaller than 1 xcexcm, and more preferably not smaller than 2 xcexcm.
(7) A single-headed piston according to any one of the above modes (1)-(6), wherein a quotient obtained by dividing a dimension r1 between a surface of extension of the cylindrical surface and the straight line which is parallel to the surface of extension and which passes one of opposite ends of the curved surface which is remote from the cylindrical surface, by an axial dimension l1 of the curved surface as measured in a direction parallel to the centerline of the cylindrical surface, is substantially equal to a quotient obtained by dividing a clearance r2 between the outer circumferential surface of the head portion of the piston and the inner circumferential surface of the cylinder bore when the piston is fitted in the cylinder bore, by an axial dimension l2 of the cylindrical surface, the clearance r2 being a difference between a diameter of the outer circumferential surface of the head portion and a diameter of the inner circumferential surface of the cylinder bore.
When the piston is inclined within the cylinder bore due to a side force which is applied from the swash plate to the piston in a direction perpendicular to its centerline, an intermediate portion of the curved surface of the head portion as seen in a direction parallel to the centerline of the cylindrical surface contacts the inner circumferential surface of the cylinder bore. Accordingly, the present arrangement assures a smooth sliding of the outer circumferential surface of the head portion of the piston on the inner circumferential surface of the cylinder bore. The above-indicated axial dimension l2 of the cylindrical surface is an axial distance between a boundary of the cylindrical surface and the curved surface which contacts the inner circumferential surface of the cylinder bore when the piston is inclined within the cylinder bore due to the above-indicated side force, and one of opposite axial ends of the cylindrical surface which is spaced from the above-indicated boundary in the diametric direction of the head portion of the piston and which is remote from the boundary in the axial direction of the head portion. The angle of inclination of the head portion of the piston is determined depending upon the axial dimension l2 of the cylindrical surface of the head portion and the clearance between the outer circumferential surface of the head portion of the piston and the inner circumferential surface of the cylinder bore when the head portion of the piston is fitted in the cylinder bore. This clearance will be hereinafter referred to as a xe2x80x9cfitting clearancexe2x80x9d. Further, the angle of inclination of the head portion of the piston within the cylinder bore determined as described above determines the manner in which the curved surface contacts the inner circumferential surface of the cylinder bore. In essence, the axial dimension l2 of the cylindrical surface is determined such that a wedge-shaped gap, which has a suitable size for facilitating introduction of the lubricant oil thereinto, is formed between the curved surface and the inner circumferential surface of the cylinder bore when the head portion of the piston is inclined in the cylinder bore.
As described above, the axial dimension l2 of the cylindrical surface determines the angle of inclination of the head portion of the piston in the cylinder bore. Even when the cylindrical surface has an opening or openings or is not continuously formed between its opposite axial ends, the axial dimension l2 of the cylindrical surface is an axial distance between the opposite axial ends.
(8) A single-headed piston according to any one of the above modes (1)-(7), wherein the axial dimension l1 of the curved surface which is parallel to its centerline is not larger than ⅕ of the axial dimension l2 of the cylindrical surface.
The axial dimension l2 of the cylindrical surface decreases and the angle of inclination of the head portion within the cylinder bore increases with an increase of the axial dimension l1 of the curved surface. Accordingly, it is not desirable that the axial dimension l1 of the curved surface is too large. In view of this, the axial dimension l1 of the curved surface is preferably not larger than ⅕, not larger than xe2x85x9, or not larger than {fraction (1/15)} of the axial dimension l2 of the cylindrical surface. It is not desirable, however, that the axial dimension l1 of the curved surface is too small. In view of this, the axial dimension l1 of the curved surface is preferably not smaller than {fraction (1/100)} of the axial dimension l2 of the cylindrical surface.
(9) A single-headed piston according to any one of the above modes (1)-(8), wherein the outer circumferential surface of the head portion includes a tapered surface which smoothly extends from one of opposite ends of the curved surface which is remote from the cylindrical surface such that the tapered surface has a diameter which gradually and linearly reduces in an axial direction of the cylindrical surface from the curved surface toward the corresponding axial end of the piston, the tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 xcexcm and 15 xcexcm.
The tapered surface cooperates with the curved surface to define the wedge-shaped gap which facilitates introduction of the lubricant oil thereinto. Accordingly, the taper angle of the tapered surface is considerably smaller than that of a chamfer formed adjacent to the tapered surface. Accordingly, the tapered surface is formed such that the difference between the radius of the large-diameter end and the radius of the small-diameter end, in other words, a half of a difference between a diameter D1 of the large-diameter end a diameter D2 of the small-diameter end, is generally in a range between 1 xcexcm and 15 xcexcm, and more preferably in a range between 2 xcexcm and 5 xcexcm.
(10) A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that: the outer circumferential surface of the head portion includes a cylindrical surface, and a tapered surface which is formed adjacent to at least one of axially opposite ends of the cylindrical surface so as to extend from at least one circumferential part of the cylindrical surface, the tapered surface being formed such that a difference between a radius of its large-diameter end and a radius of its small-diameter end is selected within a range between 1 xcexcm and 15 xcexcm.
The tapered surface which is formed adjacent to at least one of opposite ends of the cylindrical surface of the head portion of the piston is effective to reduce the noise of the compressor during its operation since the head portion of the piston smoothly slides within the cylinder bore owing to the tapered surface. The reduction of the operating noise of the compressor is achieved even when an area of boundary between the tapered surface and the cylindrical surface is not substantially rounded, as well as when the area of boundary is substantially rounded. This is because an angle between the tapered surface and the cylindrical surface is considerably close to 180xc2x0. Further, the introduction of the lubricant oil into the wedge-shaped gap formed between the tapered surface and the inner circumferential surface of the cylinder bore prevents contact of a line of intersection of the tapered surface and the cylindrical surface, with the inner circumferential surface of the cylinder bore, or reduces the contacting surface pressure between the tapered surface and the cylindrical surface.
(11) A single-headed piston according to any one of the above modes (1)-(10), wherein the head portion of the piston has a hollow cylindrical shape.
When the head portion of the piston has a hollow cylindrical shape, the weight of the piston can be easily reduced, resulting in reduction of the operating noise of the compressor. Further, the curved surface can be easily formed over the entire circumference at each of the opposite ends of the cylindrical surface, since the hollow cylindrical head portion has at its opposite axial ends a simple circular shape in transverse cross section.
(12) A single-headed piston according to any one of the above modes (1)-(10), wherein the head portion of the piston includes a sealing section having a circular cross sectional shape, and two auxiliary sliding surfaces which are located between the engaging portion of the piston and the sealing section and which consist of an inner auxiliary sliding surface which is nearer to an axis of rotation of the swash plate, and an outer auxiliary sliding surface which is remote from the axis of rotation of the swash plate, the two auxiliary sliding surfaces are flush with an outer circumferential surface of the sealing section.
In the piston according to this arrangement, the auxiliary sliding surfaces cooperate with the outer circumferential surface of the sealing section to form the outer circumferential surface of the head portion of the piston. Accordingly, when the curved surface is formed at one of opposite ends of the outer circumferential surface of the head portion on the side of the engaging portion, the curved surface is formed at one of opposite ends of each of the auxiliary sliding surfaces, which is located on the side of the engaging portion.
(13) A swash plate type compressor comprising: a housing having a plurality of cylinder bores, a rotary drive shaft which is rotatably supported by the housing, a swash plate which is prevented from rotating relative to the rotary drive shaft and which is inclined with respect to an axis of the rotary drive shaft; and a piston including a head portion slidably fitted in each of the cylinder bores, and an engaging portion slidably engaging the swash plate through a pair of shoes which are held in contact with opposite surfaces of the swash plate at a radially outer portion of the swash plate, and wherein the piston has a structure as defined in any one of the above modes (1)-(l2).
(14) A swash plate type compressor according to the above mode (14), further comprising a swash plate angle adjusting device for adjusting an angle of inclination of the swash plate with respect to the axis of the rotary drive shaft.
A swash plate type compressor wherein the angle of inclination of the swash plate is variable, in particular, a variable capacity type swash plate compressor having the above-indicated swash plate angle adjusting device which is adapted to control the inclination angle of the swash plate by controlling the pressure in the crank chamber, suffers from a serious problem of the operating noise. The piston constructed according to the present invention described above is effective to solve such a problem when applied to the above-described variable capacity type awash plate compressor having the inclination angle adjusting device.